An audio/video information system for recording and playing back audio/video information has been described in U.S. Pat. Nos. 3,842,194 and 3,842,217 to Clemens. According to this system, audio and video information are recorded in the form of geometric variations in spiral grooves on the surface of a disc. Disc replicas are then made of an insulating material such as vinyl and are coated first with a conductive film, then with a dielectric film and finally with a lubricant layer. A metallized stylus is utilized as a second electrode forming a capacitor with the video disc. The audio/video information is monitored by the stylus which detects changes in capacitance between the stylus and the video disc as the geometric variations in the form of depressions pass under the stylus.
The conductive layers are deposited such as described in U.S. Pat. No. 3,982,066 to Nyman et al, herein incorporated by reference; the dielectric layers are deposited such as described in U.S. Pat. No. 3,843,399 to Kaplan et al and U.S. Pat. No. 3,901,994 to Mehalso et al which patents are herein incorporated by reference; and the lubricant layers are deposited such as described in U.S. Pat. No. 3,833,408 to Matthies which is herein incorporated by reference.
The dielectric layers employed in the above mentioned patents are organic layers such as poly-p-xylene and organic layers formed from the deposition of styrene in a glow discharge. The major disadvantages with these organic layers are chemical and physical instability, difficulty in characterization, poor adhesion to the conductive layers and lack of interdisc and intradisc uniformity. Furthermore, the chemical and physical instability contributes to lubrication failure which results in premature wear of the disc surface and in increased wear of the stylus.
To avoid the problems associated with organic dielectric layers, attempts have been made to utilize inorganic dielectric layers such as silicon oxides. Layers of silicon oxide such as silicon dioxide can be deposited in a glow discharge by one of the following reaction mechanisms. EQU Si(OC.sub.2 H.sub.5).sub.4 (v)+4,5O.sub.2 (g).fwdarw.SiO.sub.2 +by products (CO,CO.sub.2,H.sub.2 O,H.sub.2)(g,v) (1) EQU SiH.sub.4 (g)+4,5N.sub.2 O(g).fwdarw.SiO.sub.2 +by products (NO,H.sub.2,H.sub.2 O,N.sub.2)(g,v) (2)
These deposition methods have been widely reported in the art by such authors as S. P. Mukherjee and P. E. Evans, Thin Solid Films, Vol. 14, 105 (1972); D. R. Secrist and J. D. MacKenzie, J. Electrochem Soc., Vol. 113, 914 (1966); R. J. Joyce, H. F. Sterling and J. H. Alexander, Thin Solid Films, Vol. 1, 481 (1967/68); D. M. Brown, P. V. Gray, K. F. Hauman, H. R. Phillipp and E. A. Taft, J. Electrochem Soc., Solid State Science, Vol. 115, 311 (1968); D. R. Secrist and J. D. MacKenzie, Solid State Electronics, Vol. 9, 180 (1966); and S. W. Ing, Jr. and W. Davern J. Electrochem Soc., Vol. 112, 284 (1965).
These reaction methods, however, have disadvantages when employed for depositing silicon dioxide dielectric layers on video discs. The reaction of equation (1) produces a large quantity of gaseous by-products which limit the rate at which silicon dioxide dielectric layers may be deposited. The reaction of equation (2) allows for higher deposition rates, but this method has been found to produce a silicon dioxide layer which causes excessive wear of the stylus.